The senses. We define sight, sound, smell, and touch. We do not define a separate sense for taste, since it would add nothing to our model: you can taste something if and only if you can touch it.

To add a new sense, you must do the following:

- Define the sense object itself, in parallel to the senses defined below.

- Modify class Material to set the default transparency level for this sense by defining the property xxxThru - for most senses, the default transparency level is 'opaque', but you must decide on the appropriate default for your new sense.

- Modify class Thing to set the default xxxSize setting, if desired.

- Modify class Thing to set the default xxxPresence setting, if desired.

- Modify each instance of class 'Material' that should have a non-default transparency for the sense by defining the property xxxThru for the material.

- Modify class Actor to add the sense to the default mySenses list; this is only necessary if the sense is one that all actors should have by default.